Catheter with serially connected sensing structures and methods of calibration and detection

ABSTRACT

A catheter is responsive to external and internal magnetic field generators for generating signals representing position and pressure data, with a reduced number of sensing coil leads for minimizing lead breakage and failure. The catheter includes a flexible joint with pressure sensing and position coils, at least pair of a pressure sensing coil and a position coil are serially connected. Methods of calibrating a catheter for position and pressure sensing, and detecting magnetic field interference with one catheter by another catheter or other metal or ferrous object advantageously use signals between two sets of sensors as a “back up” or “error check”.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of and claims priority to and thebenefit of U.S. application Ser. No. 14/960,273 filed Dec. 4, 2015,issued as U.S. Pat. No. 9,492,639, which is a continuation of U.S.application Ser. No. 13/732,324, filed Dec. 31, 2012, issued as U.S.Pat. No. 9,204,841, the entire content of which is incorporated hereinby reference.

FIELD OF INVENTION

The present invention relates to catheters, particularly catheters withlocation/orientation and pressure sensing capabilities.

BACKGROUND OF INVENTION

In some diagnostic and therapeutic techniques, a catheter is insertedinto a chamber of the heart and brought into contact with the innerheart wall. For example, in intracardiac radio-frequency (RF) ablation,a catheter having an electrode at its distal tip is inserted through thepatient's vascular system into a chamber of the heart. The electrode isbrought into contact with a site (or sites) on the endocardium, andelectrical activity in the heart chamber is detected by the electrode.Moreover, RF energy may be applied through the catheter to the electrodein order to ablate the heart tissue at the site.

Catheters for mapping and/or ablation typically carry one or moremagnetic position sensors for generating signals that are used todetermine position coordinates of a distal portion of catheter. For thispurpose, magnetic field generators are driven to generate magneticfields in the vicinity of the patient. Typically, the field generatorscomprise coils, which are placed below the patient's torso at knownpositions external to the patient. These coils generate magnetic fieldsthat are sensed by the magnetic position sensor(s) carried in thecatheter. The sensor(s) generate electrical signals that are passed to asignal processor via leads that extend through the catheter.

Proper contact between the electrode and the endocardium is necessary inorder to achieve the desired diagnostic function and therapeutic effectof the catheter. Excessive pressure, however, may cause undesired damageto the heart tissue and even perforation of the heart wall. For pressuresensing, a catheter typically carries a miniature transmitting coil andthree sensing coils on opposing portions of a flexibly-jointed distaltip section. The transmitting coil is aligned with the longitudinal axisof the catheter and three sensing coils are also aligned with thelongitudinal axis but positioned at an equal distance from thetransmitting coil, and at equally-spaced radial positions about thelongitudinal axis of the catheter. The miniature transmitting coilgenerates a magnetic field sensed by the three sensing coils whichgenerate signals representative of axial displacement and angulardeflection between the opposing portions of the distal tip section.

The axes of the sensing coils are parallel to the catheter axis (andthus to one another, when the joint is undeflected). Consequently, thesensing coils are configured to output strong signals in response to thefield generated by the miniature field generator. The signals varystrongly with the distances of the coils. Angular deflection of thedistal portion carrying the miniature field generator gives rise to adifferential change in the signals output by sensing coils, depending onthe direction and magnitude of deflection, since one or two of thesecoils move relatively closer to the field generator. Compressivedisplacement of the distal portion gives rise to an increase in thesignals from all of three sensing coils. Prior calibration of therelation between pressure on distal portion and movement of joint may beused by processor in translating the coil signals into terms ofpressure. By virtue of the combined sensing of displacement anddeflection, the sensors read the pressure correctly regardless ofwhether the electrode engages the endocardium head-on or at an angle.

With position sensing and pressure sensing, a conventional catheter maycarry six leads, one for each of the three position sensing coils andthe three pressure sensing coil, with each lead being a twisted pair ofwires. Leads are time-consuming and expensive to manufacture andinstall. Moreover, the leads occupy space in the space-constrainedcatheter tip and are susceptible to breakage. A reduction in the numberof leads used in the catheter and/or their lengths would provide anumber of benefits, including reduced catheter production time,increased total catheter yield, and reduced production costs.

Some catheterization procedures require the use of a second catheter inclose proximity to a first catheter. Shaft Proximity Interference(“SPI”) occurs when metal components of the second catheter disturbsensing coils in the first catheter. For example, where a pressuresensing coil reacts to changes in the magnetic field due to errantmagnetic interference by an adjacent catheter instead of physicaldistortion of a distal tip due to tissue contact, signals from the coilcan mislead an operator relying a catheterization system processingthose signals.

Accordingly, it is desirable to provide a catheter with combined orsimplified position and pressure sensing capabilities for reducing thenumber of sensor coil leads and/or their lengths. It is also desirableto provide a catheter capable of recognizing distortions in magneticfields caused by factors other than physical distortion of the distaltip due to tissue contact.

SUMMARY OF THE INVENTION

The present invention is directed to a catheter responsive to externaland internal magnetic field generators for generating position data todetermine position of the catheter within a sensing volume of magneticfields and pressure data to determine pressured exerted on a distal endof the catheter when engaged with tissue, with a reduced number ofsensing coil leads for minimizing lead breakage and failure.

In one embodiment, the catheter includes a distal section adapted forengagement with patient tissue, where the distal section has a proximalportion, a distal portion and a flexible joint. Either of the proximalportion or the distal portion carries an internal magnetic fieldgenerator and the other of the proximal portion or the distal portioncarries a plurality of first sensing coils and a plurality of secondsensing coils, where each of the first sensing coils is axially alignedwith the field generator and sensitive to the internal magnetic fieldgenerator for generating signals representative of pressure exerted onthe distal section, and where each of the second sensing coils ismutually orthogonal to each other and sensitive to each of a pluralityof external magnetic field generators for generating signalsrepresentative of position of the distal section, where at least onefirst sensing coil and one second sensing coil are connected to eachother by a lead.

In one embodiment, there are three first sensing coils and two secondsensing coils.

In one embodiment, the first sensing coils are adapted to generatesignals representative of pressure exerted on the distal section and thesecond sensing coils are adapted to generate signals representative ofposition of the distal section.

In one embodiment, a first sensing coil is also sensitive to each of theexternal magnetic field generators for generating signals representativeof position of the distal section.

In one embodiment, there are a first pair of first and second sensingcoils connected by one lead and a second pair of first and secondsensing coils connected by a second lead.

In one embodiment, the flexible joint includes a resilient memberadapted to allow axial displacement and angular deflection between theproximal and distal portions of the distal section.

In one embodiment, each magnetic field is distinguishable by frequency,phase and/or time.

The present invention is also directed to a method of calibrating acatheter for position and pressure sensing and a method of detectingmagnetic field interference with one catheter by another catheter orother metal or ferrous object. The present invention advantageously usessignals from the sensors Sx and Sy as a “back up” or “error check”. Apressure calibration is performed on the catheter during manufacturingand production. By identifying deformation characteristics of the distalsection, applying known magnitudes of force on the distal sectionportion at a variety of selected angles (e.g., compressive loads, axialloads, etc.) and measuring axial displacement and angular deflection, acalibration file on the signals that may be generated by pressuresensors in response to the magnetic field generated by the internalfield generator MF is compiled as a first file and stored in memory.Simultaneously, a calibration file on the signals that may be generatedby position sensors in response to the magnetic field generated by theinternal field generator MF is compiled as a second file and stored inmemory. While the catheter is in use in a patient's body, signals fromthe pressure sensors in response to internal field generator MF arereferenced against the first file stored in memory to obtain axialdisplacement and angular deflection data for outputting catheterpressure data to the operator. Advantageously, signals from positionsthat include signals in response to the internal field generator MF arereferenced against the second file for detecting and identifyingdiscrepancies. If a discrepancy is determined, providing an indicationto user of the discrepancy.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic, pictorial illustration of a catheter-basedmedical system, in accordance with an embodiment of the presentinvention.

FIG. 2 is a side view of a catheter for use with the system of FIG. 1,in accordance with an embodiment of the present invention.

FIG. 3 is a schematic, cutaway view showing details of the distalsection of the catheter of FIG. 2.

FIG. 4 is a schematic detail view showing the distal section of FIG. 3in contact with endocardial tissue.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a system and catheter for cardiaccatheterization, where the catheter has a sensing assembly that providessignals representative of both position of the catheter and pressureexerted on a distal section of the catheter when it engages tissue.Compared to conventional position sensing assemblies and pressuresensing assemblies, sensing assemblies of the catheter areadvantageously configured with serially-wired sensing structures toreduce the number of leads and/or their lengths for a simplifiedcatheter structure that minimizes the risk of damaged or broken leads.

FIG. 1 is a schematic, pictorial illustration of a conventional system20 for cardiac catheterization as known in the art. System 20 may bebased, for example, on the CARTO™ system, produced by Biosense WebsterInc. (Diamond Bar, Calif.). This system comprises an invasive probe inthe form of a catheter 28 and a control console 34. In the embodimentdescribed hereinbelow, it is assumed that catheter 28 is used inablating endocardial tissue, as is known in the art. Alternatively, thecatheter may be used, mutatis mutandis, for other therapeutic and/ordiagnostic purposes in the heart or in other body organs. As shown inFIG. 2, the catheter 28 comprises an elongated catheter body 11, adeflectable intermediate section 12, a distal section 13 carrying atleast a tip electrode 15 on its distal tip end 30, and a control handle16.

An operator 26, such as a cardiologist, inserts catheter 28 through thevascular system of a patient 24 so that a distal section 13 of thecatheter enters a chamber of the patient's heart 22. The operatoradvances the catheter so that a distal tip 30 of the catheter engagesendocardial tissue 70 at a desired location or locations. Catheter 28 isconnected by a suitable connector at its proximal end to console 34. Theconsole may comprise a radio frequency (RF) generator, which supplieshigh-frequency electrical energy via the catheter for ablating tissue inthe heart at the locations engaged by the distal section 13.Alternatively or additionally, the catheter and system may be configuredto perform other therapeutic and diagnostic procedures that are known inthe art.

Console 34 uses magnetic sensing to determine pressure and positiondata, including (i) axial displacement and angular deflection of thedistal section 13 due to pressure from contact with endocardial tissue70, and (ii) position coordinates of the distal section 13 in the heart.For the purpose of generating pressure data, including axialdisplacement and angular deflection of the distal section 13 of thecatheter 28, the driver circuit 38 in console 34 drives a miniaturemagnetic field generator MF housed in a distal portion 13D of the tipsection 13, as shown in FIG. 3. In the disclosed embodiment, the fieldgenerator MF comprises a coil whose axis is aligned with the Z axiscoaxial with a longitudinal axis 25 of the catheter.

For detecting and measuring pressure, the distal section 13 has aproximal portion 13P and a distal portion 13D which are connected toeach other by a flexible and elastic joint 54 which may be constructedof any suitable material(s) with the desired flexibility and strength.The resilient joint 54 permits a limited range of relative movementbetween the portions 13P and 13D in response to forces exerted on thedistal section 13. Such forces are encountered when the distal tip end30 is pressed against the endocardium during an ablation procedure. Asshown in FIG. 4, the distal end 30 of catheter 28 is in contact withendocardium 70 of heart 22, in accordance with an embodiment of thepresent invention. Pressure exerted by the distal tip end 30 against theendocardium deforms the endocardial tissue slightly, so that the tipelectrode 15 contacts the tissue over a relatively large area. Since theelectrode engages the endocardium at an angle, rather than head-on, thedistal portion 13D bends at joint 54 relative to the proximal portion13P. The bend facilitates optimal contact between the electrode 15 andthe endocardial tissue 70.

As shown in FIG. 3, the joint 54 comprises an outer tubing 56 which maybe the outer tubing 55 of the distal section 13 which is constructed ofa flexible, insulating material, such as Celcon®, Teflon®, orheat-resistant polyurethane. Or, the tubing 56 may be of a materialspecially adapted to permit unimpeded bending and compression of thejoint. (This material is cut away in FIG. 3 in order to expose theinternal structure of the catheter.) The distal section 13D is typicallyrelatively rigid, by comparison with the remainder of the catheter.

The joint 54 further comprises a resilient coupling member 60, such as acoil spring, or a tubular piece of an elastic material with a helicalcut along a portion of its length. For example, the coupling member maycomprise a polymer, such as silicone, polyurethane, or other plastics,or a superelastic alloy, such as nickel titanium (Nitinol). The helicalcut causes the tubular piece to behave like a spring in response toforces exerted on distal portion 13D. Further details regarding thefabrication and characteristics of this sort of coupling member arepresented in U.S. Publication No. 2009/0306550, which is assigned to theapplicant of the present patent application and whose disclosure isincorporated herein by reference. Alternatively, the coupling member maycomprise any other suitable sort of resilient component with the desiredflexibility and strength characteristics.

The stiffness of the coupling member 60 determines the range of relativemovement between distal portions 13P and 13D in response to forcesexerted on the distal portion 13D. Such forces are encountered when thedistal tip end 30 is pressed against the endocardium during a mappingand/or ablation procedure. The desired pressure for good electricalcontact between the distal portion 13D and the endocardium duringablation is on the order of 20-30 grams. The coupling member 60 isconfigured to permit axial displacement (i.e., lateral movement alongthe longitudinal axis 25 of catheter 28) and angular deflection of thedistal portion 13D in proportion to the pressure on the distal tip end30. Measurement of the displacement and deflection gives an indicationof the pressure and thus helps to ensure that the correct pressure isapplied during ablation.

An electromagnetic or magnetic field is transmitted by an internal fieldgenerator MF housed in the distal portion 13D for sensing and detectionby a first sensor 17 assembly housed in the proximal portion 13P. In theillustrated embodiment, the first sensor assembly 17 includes sensorcoils S1, S2 and S3 located in the proximal portion 13D of the distalsection 13. Each of these coils is generally parallel with the Z axis orlongitudinal axis 25. The three coils are all located in a first axialsection at different azimuthal angles about the longitudinal axis 25 orZ axis, where an axial plane is defined herein as a plane perpendicularto the catheter longitudinal or Z axis and an axial section is definedherein as being contained within two axial planes of the catheter. Thethree coils may be spaced azimuthally 120 degrees apart at the sameradial distance from the axis.

Axial displacement and/or angular deflection of the distal portion 13Drelative to the proximal portion 13P gives rise to a differential changein the signal outputs by the coils S1, S2 and S3, depending on thedirection and magnitude of deflection, since one or two of these coilsmove relatively closer to the field generator MF. Compressivedisplacement of the distal portion 13D gives rise to an increase in thesignals from each of coils S1, S2 and S3. Changes in the sensing of themagnetic field by generator MF causes the coils S1, S2 and S3 togenerate electrical signals, with amplitudes that are indicative of suchaxial displacement and/or angular deflection. A signal processor 36receives and processes the signals generated by the coils S1, S2 and S3,in order to derive an indication of the pressure exerted by the distalsection 13 on the endocardium 70.

For the purpose of generating position data or coordinates, a drivercircuit 38 in console 34 drives external magnetic field generators, forexample, F1, F2 and F3, to generate magnetic fields in the vicinity ofthe body of patient 24 and define an external frame of reference Thegenerators F1, F2 and F3 are comprised of coils, which are placed belowthe patient's torso at known positions external to the patient. Thesecoils generate magnetic fields within the patient's body in a predefinedworking volume that contains heart 22.

A second sensor assembly 18 is housed in the proximal portion 13P,proximal of the first sensor assembly 17, to respond to the fieldgenerators F1, F2 and F3 and generate electrical signals. In theillustrated embodiment, the sensor assembly 18 includes at least twominiature sensor coils Sx and Sy wound on air coils. The coils havegenerally mutually orthogonal axes with each other and with at least onecoil of the first sensor assembly 17, for example, the coil S1.Accordingly, the coil Sx is aligned with an X axis and the coil Sy isaligned with a Y axis, and both coils are orthogonal to the coil S1aligned with the Z axis within an (X,Y,Z) coordinate system.

The two coils Sx and Sy are located in a second axial section (e.g.,proximal of the first axial section of the first sensor assembly 17) atdifferent azimuthal angles about the longitudinal axis 25 or Z axis,where an axial plane is defined herein as a plane perpendicular to thecatheter longitudinal or Z axis and an axial plane is defined herein asbeing contained within two axial planes of the catheter. The two coilsmay be spaced azimuthally 120 degrees apart from each other and relativeto the sensor coil S1 of the first sensor assembly 17, at the sameradial distance from the axis.

Electromagnetic or magnetic fields are generated by the external fieldgenerators F1, F2, F3 and sensed by the sensor coils S1, Sx and Sy fordetecting position of the catheter. The magnetic fields created by thefield generators F1, F2 and F3 cause the coils S1, Sx and Sy to generateelectrical signals, with amplitudes that are indicative of the positionof the distal section 13 relative to the fixed frame of reference offield generators F1, F2 and F3. In one embodiment, the three fieldgenerators F1, F2 and F3 generates a magnetic field composed of threedifferently-oriented field components. Each of these field components issensed by each sensor coil S1, Sx and Sy, each of which produces asignal composed of three components.

As shown in FIG. 1, the signal processor 36 of the console 34 processesthese signals from the coils S1, Sx and Sy in order to determine theposition coordinates of the distal section 13, typically including bothlocation and orientation coordinates. A similar method of positionsensing is implemented in the above-mentioned CARTO system and isdescribed in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118,6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO96/05768, and in U.S. Patent Application Publications 2002/0065455 A1,2003/0120150 A1 and 2004/0068178 A1, all of whose disclosures areincorporated herein by reference.

Signals from the sensors of the first sensor assembly 17 and the secondsensor assembly 18 are transmitted to the signal processor 36 via leads.In accordance with a feature of the present invention, selected sensorsfrom the first sensor assembly 17 and the second sensor assembly 18 areserially connected and share a common lead for transmitting theirsignals to the signal processor. In the illustrated embodiment of FIG.3, leads 63, 64A and 65A extend respectively from the sensors S1, S2 andS3. The lead 63 extends from the sensor S1 to the signal processor 36.The lead 64A extends from the sensor S2 to the sensor Sx, seriallyconnecting these sensors. The lead 65A extends from the sensor S3 to thesensor Sy, serially connecting these sensors.

As described above, each of the sensors S1, S2 and S3 generates signalsrepresentative of pressure (including axial displacement and angulardeflection) of the distal section 13 obtained from sensing of themagnetic field generated by the internal field generator MF. As alsodescribed above, each of the sensors S1, Sx and Sy generates signalsrepresentative of position of the distal section obtained from sensingof each magnetic field generated by the external field generators F1, F2and F3.

Accordingly, the lead 63 transmits to the signal processor 36 signalsgenerated by the sensor S1 representative of pressure. The lead 64Btransmits to the signal processor 36 both signals generated by thesensor S2 representative of pressure and signals generated by the sensorSx representative of position. The lead 65B transmits to the signalprocessor 36 both signals generated by the sensor S3 representative ofpressure and signals generated by sensor Sy representative of position.The resulting combined signals transmitted by leads 64B and by 65Bcreate common sums which may be separated by electronic filtering whereoperating frequencies of position and force sensing are suitablyseparated in frequency space, as understood by one of ordinary skill inthe art.

As such, the signal processor 36 is advantageously connected to onlythree leads, namely, 63, 64B and 65B for receiving signals from the fivesensors for position and pressure sensing compared to the typical fiveor six leads of a conventional catheter with five or six position andpressure sensors. Moreover, the leads 64A and 65A serially connectingpaired sensors are significantly shorter in length.

Each lead is time-consuming and expensive to manufacture and assemble ina catheter. Moreover, leads occupy space in a space-constrainedcatheter. Leads are also susceptible to breakage. Having a reducednumber or length of leads transmitting signals to the signal processorprovides a number of benefits, including reduced catheter productiontime, increased total catheter yield, and reduced production costs.

It is understood that different pairings of sensors for serial wiring orconnection are provided by the present invention. In alternateembodiments, for example, the sensors S1 and Sx, and the sensors S2 andSy may be serially connected, or the sensors S3 and Sx and the sensorsS1 and Sy may be serially connected. For the sensors S1, S2, S3, Sx andSy, there are six possible permutations of pairing, of which there maybe one serially connected pair or two serially connected pairs in thedistal section 13.

Because the coil of the generator MF in the distal portion 13D isradially symmetrical, it is well suited for on-axis alignment with thelongitudinal axis 25 of the catheter. However, it is understood that thecoil may also be off-axis as desired or appropriate, with the furtherunderstanding that tilting the coil off-axis will both improve certaincoil(s) and degrade other coil(s) of mutually orthogonal sensors.

It is also understood that the coils of the first and second sensorassemblies 17 and 18 may be of any suitable size and shape provided theyconform to packaging constraints within the distal section 13 ofalignment and/or mutual orthogonality. Conventional pressure sensorstend to be cylindrical, that is, longer and narrower, because of Z axisalignment with the generator MF within the distal section, whereasconventional X and Y position sensors tend to be more elliptical so asto maintain mutual orthogonality with the Z position sensor andconformity with the packaging constraints of the distal section. In thedisclosed embodiment of the present invention, the sensors S1, S2 and S3are configured more as a conventional pressure sensor and thus arerelatively longer and narrower, whereas the sensors Sx and Sy areconfigured more as conventional position sensors and thus are moreelliptical. Position sensors and pressure sensors are described in U.S.Pat. No. 6,690,963 and U.S. Publication No. 20090138007, the entiredisclosures of which are incorporated herein by reference. In theillustrated embodiment, the sensor coils S1, S2 and S3 are configured asposition sensors, and the sensor coils Sx and Sy are configured aspressure sensors.

The magnetic fields generated by each field generator F1, F2, F3 and MFare distinguishable with regard to different parameters, includingfrequency, phase and/or time, and the signals generated by each sensorcoil S1, S2, S3, Sx and Sy from measuring the magnetic field fluxresulting from these distinguishable magnetic fields are similarlydistinguishable. Frequency, phase and/or time multiplexing is applied asappropriate or desired. For example, the current to pressure-sensingfield generator MF may be generated at a selected frequency in the rangebetween about 16 kHz and 25 kHz, while position field generators F1, F2and F3 are driven at different frequencies

The signal processor 36 processes these signals in order to determinedata, including (i) the position coordinates of the distal section 13,typically including both location and orientation coordinates, and (ii)axial displacement and angular deflection of the distal section 13. Thesignal processor 36 may comprise a general-purpose computer, withsuitable front end and interface circuits for receiving signals fromcatheter 28 and controlling the other components of console 34. Theprocessor may be programmed in software to carry out the functions thatare described herein. The software may be downloaded to console 34 inelectronic form, over a network, for example, or it may be provided ontangible media, such as optical, magnetic or electronic memory media.Alternatively, some or all of the functions of processor 36 may becarried out by dedicated or programmable digital hardware components.Based on the signals received from the catheter and other components ofsystem 20, processor 36 drives a display 42 to give operator 26 visualfeedback regarding the position of distal end 30 in the patient's body,as well as axial displacement and angular deflection of the distal tipof the catheter, and status information and guidance regarding theprocedure that is in progress.

The processor 36 receives these signals via the leads 63, 64B and 65Bextending through catheter 28, and processes the signals in order toderive the location and orientation coordinates of the distal section 13in this fixed frame of reference, and to derive pressure information,including axial displacement and angular deflection of the distalsection. The disposition of the coils S1, S2, S3, Sx and Sy and pressureexerted on the distal portion 13D of the distal section 13 can becalculated from the characteristics of the fields, such as strength anddirection, as detected by the coils. Thus, the field generators F1, F2,F3 and MF and the sensing coils S1, S2, S3, Sx and Sy cooperativelydefine a plurality of transmitter-receiver pairs, wherein each such pairincludes one field generator and a coil as elements of the pair, witheach coil disposed at a different position or orientation from the othercoils. By detecting the characteristics of field transmissions betweenthe elements of the various pairs, the system de-convolves position andpressure data from the serially-connected sensors to deduce informationrelating to the disposition of the distal section 13 in the externalframe of reference as defined by the field generators F1, F2, and F3 andinformation relating to pressure exerted on the distal section MF assensed within the magnetic field generated by field generator MF. Theposition information can include the position of the distal section 13,the orientation of the distal section 13, or both. As understood by oneof ordinary skill in the art, the calculation of position informationrelies upon the field generators F1, F2 and F3 being positioned in knownpositions and orientations relative to one another, and the calculationof pressure based on axial displacement and angular deflection reliesupon the field generator MF and the sensing coils S1, S1 and S3 being inknown positions and orientations relative to each other.

The field generating coils F1, F2, F3 and MF are one type of magnetictransducer that may be used in embodiments of the present invention. A“magnetic transducer,” in the context of the present patent applicationand in the claims, means a device that generates a magnetic field inresponse to an applied electrical current and/or outputs an electricalsignal in response to an applied magnetic field. Although theembodiments described herein use coils as magnetic transducers, othertypes of magnetic transducers may be used in alternative embodiments, aswill be apparent to those skilled in the art.

Various other configurations of the coils in the sensing assemblies mayalso be used, in addition to the configuration shown and describedabove. For example, the positions of the field generator MF and thecoils S1, S2 and S3 may be reversed, so that that field generator coilMF is in the proximal portion 13D, proximal of joint 54, and the sensorcoils are in the distal portion 13D. As another alternative, coils S1,S2 and S3 may be driven as field generators (using time- and/orfrequency-multiplexing to distinguish the fields), while field generatorcoil MF serves as the sensor. The sizes and shapes of the transmittingand sensing coils in FIG. 3 are shown only by way of example, and largeror smaller numbers of coils may similarly be used, in various differentpositions, so long as one of the assemblies comprises at least twocoils, in different radial positions, to allow differential measurementof joint deflection.

In accordance with another feature of the present invention, while thecoils Sx and Sy are orthogonal to and not aligned with the axis of theminiature field generator MF, its magnetic dipole field lines allowdetection by the orthogonal coils Sx and Sy. While the coils Sx and SCymay sense a relatively weaker magnetic field by the field generator MF,compared to the coils S1, S2 and S3 because of their respectiveorientation relative to the field generator MF, there is sufficientsensitivity for the purpose of sensing Shaft Proximity Interference,that is, detection as to whether changes in the magnetic field of thefield generator MF as sensed by the coils S1, S2 and S3 are due tophysical distortion of the distal section 13 resulting from engagementwith tissue or merely magnetic interference from adjacent catheters ormetal or ferrous objects.

The present invention advantageously uses signals from the sensors Sxand Sy as a “back up” or “error check”. During manufacturing andassembly of the catheter 28, the signals of sensors Sx and Sy generatedin response to the internal field generator MF without disturbance fromany adjacent catheter or metal objects are calibrated and stored inmemory in the console 34. Although these signals are weaker than thosegenerated by the sensors S1, S2 and S3 in response to the internal fieldgenerator MF, these signals by Sx and Sy carry unique signatures orcharacteristics. Thus, when the catheter 28 is in use with the internalfield generator MF generating a magnetic field that is sensed by thesensing coils S1, S2 and S3 for determining pressure, the sensing coilsSx and Sy of the second sensor assembly 18 sensing the magnetic fieldsof the external field generators F1, F2 and F3 are also sensing themagnetic field by the internal field generator MF. The signal processor36 receives signals from the sensors Sx and Sy and identifies thosesignals resulting from the magnetic field of the internal fieldgenerator MF (versus those resulting from the magnetic field of theexternal field generators F1, F2 and F3) and compares them to thecalibrated signals stored in memory. If the signal processor 36 detectsa discrepancy between those signals and the calibrated signals, theconsole 34 outputs an indication of the discrepancy to the operator andmay issue a visual and/or audio alarm.

In one embodiment, a pressure calibration is performed on the distalsection 13 during manufacturing and production. By identifyingdeformation characteristics of the resilient coupling member 60,applying known magnitudes of force on the distal portion 13D at avariety of selected angles (e.g., compressive loads, axial loads, etc.)and measuring axial displacement and angular deflection, a calibrationfile on the signals that may be generated by the sensors S1, S2 and S3in response to the magnetic field generated by the internal fieldgenerator MF is compiled as a first file and stored in memory.Simultaneously, a calibration file on the signals that may be generatedby the sensors Sx and Sy in response to the magnetic field generated bythe internal field generator MF is compiled as a second file and storedin memory.

With the catheter in use in a patient's body, the signal processor 36receives signals from the sensors S1, S2 and S3 in response to internalfield generator MF and references those signals against the first filestored in memory to obtain axial displacement and angular deflectiondata for outputting catheter pressure data to the operator.Advantageously, the signal processor 36 is also receiving signals fromthe sensors Sx and Sy that include signals in response to the internalfield generator MF and referencing those signals against the second filefor detecting and identifying discrepancies.

Accordingly, the present invention includes a method of calibrating acatheter for detecting interference with magnetic field sensing causedby presence of a second catheter or other metal or ferrous object,comprising:

-   -   1) Providing a catheter with a first sensor and a second sensor        with both first and second sensors adapted to respond to a        magnetic field generated by a field generator.    -   2) Driving the field generator to enable the first and second        sensors to generate calibration signals    -   3) Applying forces of axial displacement and angular deflection        on the catheter.    -   4) Calibrating the calibration signals from the first sensor to        create a first calibration file and calibrating the calibration        signals from the second sensor to create a second calibration        file, including:        -   a. Applying forces of axial displacement and angular            deflection to the catheter.        -   b. Store in memory data representative of signals generated            by the first sensor in response to forces applied to the            catheter.        -   c. Store in memory data representative of signals generated            by the second sensor in response to forces applied to the            catheter.

The present invention also includes a method of detecting interferencewith magnetic field sensing in a first catheter caused by presence of asecond catheter or other metal or ferrous object, comprising:

-   -   1) Providing a catheter with a first sensor and a second sensor        with both first and second sensors adapted to respond to a        magnetic field generated by a field generator.    -   2) Driving the field generator to enable the first and second        sensors to generate calibration signals.    -   3) Applying forces of axial displacement and angular deflection        on the catheter.    -   4) Calibrating the calibration signals from the first sensor to        create a first calibration file and calibrating the calibration        signals from the second sensor to create a second calibration        file, including:        -   a. Applying forces of axial displacement and angular            deflection to the catheter.        -   b. Store in memory data representative of signals generated            by the first sensor in response to forces applied to the            catheter.        -   c. Store in memory data representative of signals generated            by the second sensor in response to forces applied to the            catheter.    -   5) When the catheter is in use, driving the field generator to        enable the first and second sensors to generate data signals.    -   6) Comparing the data signals from the second sensor to the        calibration signals in the second calibration file.

The method of detecting may further include:

-   -   7) Determining whether a discrepancy exists between the data        signals of the second sensor and the calibration signals in the        second calibration file.    -   8) If a discrepancy is determined, providing an indication to        user of the discrepancy.

It is understood that detection of discrepancy can be performed with orwithout serially connected sensors. That is, discrepancy detection usestwo sets of sensors, for example, the first sensor assembly 17, namely,sensors S1, S2 and S3, and the second sensor assembly 18, namely,sensors Sx and Sy in order to have a comparative indication. Where thereare serially connected sensors between the first and second sensorassemblies, the system can deconvolve the signals and data as needed.

The preceding description has been presented with reference to certainexemplary embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes to the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. It is understood that the drawings are not necessarilyto scale. Accordingly, the foregoing description should not be read aspertaining only to the precise structures described and illustrated inthe accompanying drawings. Rather, it should be read as consistent withand as support for the following claims which are to have their fullestand fairest scope.

What is claimed is:
 1. A catheter for use with a catheterization systemhaving a plurality of external magnetic field generators, eachgenerating a position-data magnetic field, comprising: a flexibletubing; and a distal section adapted for engagement with patient tissue,the distal section having: a proximal portion, a distal portion and aflexible joint between the proximal portion and the distal portion; aninternal magnetic field generator positioned in one of the proximal anddistal portions, the internal magnetic field generator generating apressure-data magnetic field; three first sensing coils and two secondsensing coils positioned in the other of the proximal and distalportions, one of the first and second sensing coils adapted to sense thepressure-data magnetic field and generate signals representative of datarelating to pressure exerted on the distal section when engaged withtissue, the other of the first and second sensing coils adapted to senseeach of the position-data magnetic fields and generate signalsrepresentative of data relating to position of the distal section; afirst lead serially connecting one of the three first sensing coils andone of the two second sensing coils; a second lead serially connecting asecond one of the three first sensing coils and a second one of the twosecond sensing coils; and a third lead connected to a third one of thethree first sensing coils.
 2. The catheter of claim 1, wherein theflexible joint includes a resilient member adapted to allow axialdisplacement and angular deflection between the proximal and distalportions of the distal section.
 3. The catheter of claim 1, wherein thesystem includes a signal processor adapted to receive signals from thefirst, second and third leads.
 4. The catheter of claim 1, wherein firstsensing coils are elliptical.
 5. The catheter of claim 1, wherein thesecond sensing coils are cylindrical.
 6. The catheter of claim 1,wherein the first sensing coils are aligned with a Z axis and each ofthe second sensing coils are orthogonal to each other and to the firstsensing coils.
 7. The catheter of claim 1, wherein the internal magneticfield generator is a transmitting coil axially aligned with alongitudinal axis of the catheter.
 8. The catheter of claim 6, whereinthe first sensing coils are aligned with the internal magnetic fieldgenerator.
 9. A catheter for use with a catheterization system having atleast three external magnetic field generators, each generating aposition-data magnetic field, comprising: a flexible tubing; and adistal section adapted for engagement with tissue, the distal sectionhaving: a proximal portion, a distal portion and a flexible jointbetween the proximal portion and the distal portion; an internalmagnetic field generator positioned in the distal portion, the internalmagnetic field generating a pressure-data magnetic field; three pressuresensing coils positioned in the proximal portion, each configured tosense the pressure-data magnetic field and generate signalsrepresentative of data relating to pressure exerted on the distalsection when engaged with tissue; two position sensing coils positionedin the proximal portion, each configured to sense each position-datamagnetic field and generate signals representative of data relating toposition of the distal section; a first lead serially connecting one ofthe three pressure sensing coils and one of the two position sensingcoils; and a second lead serially connecting a second one of the threepressure sensing coils and a second one of the two position sensingcoils; and a third lead connected to a third one of the three pressuresensing coils.
 10. The catheter of claim 9, wherein the flexible jointincludes a resilient member adapted to allow axial displacement andangular deflection between the proximal and distal portions of thedistal section.
 11. The catheter of claim 9, wherein the system includesa signal processor adapted to receive signals from the first, second andthird leads.
 12. The catheter of claim 9, wherein each magnetic field isdistinguishable by one or more of the group consisting of frequency,phase and time.
 13. The catheter of claim 9, wherein the pressuresensing coils are cylindrical.
 14. The catheter of claim 9, wherein theposition sensing coils are elliptical.